590 CYCLES OF ORGANIC AND INORGANIC SUBSTANCES 



is low. Menard and Shipek (1958) estimate that between 20% 

 and 50% of the deep-sea floor in the southwestern Pacific is 

 covered with nodules on the basis of the photographs of the 

 bottom and the occurrence of nodules in cores. Phillipsite, barite, 

 and fish debris, phases which are strongly diluted in rapidly 

 amassing deposits, are found in high concentrations in areas 

 associated with ferromanganese minerals. 



The ferromanganese minerals act as hosts for a suite of elements 

 which include copper, nickel, cobalt, zinc, lead, thorium, and the 

 rare earths. These guest metals, which are enriched in the ferro- 

 manganese minerals, as well as the manganese, exist in sea water 

 in states of undersaturation (Goldberg, 1958), and their assimila- 

 tion by these minerals has been postulated to account at least in 

 part for this situation. 



Their unique chemical composition, unlike that of any terrestrial 

 mineral has strongly indicated the authigenic character of the 

 ferromanganese accumulations (Table IV). Further support comes 

 from the lead isotopic analyses of Chow and Patterson (1959), 

 who point out that the distinctive values of the radiogenic lead 

 isotopes suggest a derivation of the lead from sea water. 



Table IW A\erage Composition of Manganese Nodules from the Pacific Ocean 

 Element Weight % 



Fe 14 



Mn 19 

 Ni 0.4 



Co 0.3 



Cu 0.5 



Ti 0.8 



Zn 0.04 



I^b 0.1 



P 0.5 



Al 0.7 



Zr 0.006 



Structural investigations by Buser and Griitter (1956) by x-ray 

 and electron microscopic techniques indicate the minerals are 

 composed of the crystalline iron and manganese compounds, 

 5-Mn02, manganites and goethite, as well as some amorphous 



